1. Field of the Invention
This invention relates to a resampling apparatus, a method, and recording medium having resampling program recorded therein for digital image.
2. Description of Related Art
For high quality transformation in conventional resampling of digital images, it is important to apply transformation original images to transformation target images effectively as much as possible.
To obtain high quality transformation consequences on image transformation, various resampling methods have been used. For example, for magnifying methods, exemplified are, as methods suppressing jaggies, such as, e.g., bilinear interpolation, and bicubic interpolation. For reducing methods, exemplified are, as methods suppressing aliasing, such as, e.g., area mean method, pre-filter, post filter, trilinear filter, and isotropic filter.
Hereinafter, those methods are described below in detail.
First, the bilinear interpolation is an interpolation method having the steps of referring total four pixels of a pixel of an image prior to transformation and adjacent pixels with respect to a concerned pixel and making weighing according to the position, to decide the respective pixels of the transformation target. This method has a slower processing speed than a nearest neighbor method but is faster than a mean pixel method. The bilinear interpolation can suppress jaggies more than the nearest neighbor method.
To the contrary, bicubic interpolation is an interpolation method similar to the bilinear interpolation but refers total sixteen pixels of the transformation original and adjacent pixels with respect to the respective pixels of the transformation target. This interpolation is, so-called, a development type bilinear interpolation, and can obtain more natural smooth image quality in comparison with the bilinear interpolation.
Transformation using such a bilinear interpolation and a bicubic interpolation is done by scanning the transformation target image basically without disparity, so that it can be used for not only magnification and reduction but also image transformation of two or more dimension represented by projective transformation, rotation, and polar conversion. As a previous concern, when a method scanning not a transformation target image but a transformation original image is used, the transformation target image may not be produced entirely, and may cause some failure at a part of pixels.
Further, the area mean method is a method referring to pixel groups of the transformation previous image corresponding to a concerned pixel to decide a pixel of the transformation target, and using the average of the pixel groups. This is so called to as a mean pixel method, and is generally a method used exclusively for reduction.
The pre-filter is a method for making smoothing according to a reduction rate before reducing images.
The post-filter is a so called super sampling method, and is a reducing method dividing a pixel of the transformation target into plural pixels, referring to pixel groups of the transformation previous image corresponding to the concerned pixel, and using the average of the pixel groups, to decide the pixel of the transformation target.
The tri-linear filter is used for drawing polygons mainly for three-dimensional graphics, and is a method preparing mipmaps with, in a stepwise manner, already contracted images utilizing mean of images, and synthesizing in application of a single or plural already contracted image or images according to the contracting rate of the images. With the tri-linear filter, common deterioration that can be seen in bilinear filter images using mipmapping can be corrected.
The isotropic filter is a method used for drawing, e.g., polygons on the three-dimensional graphics, and is a method synthesizing in application of mipmaps using a referring method in consideration of texture transformation in drawing polygons as obliquely orienting a camera. This method can be said as advanced further in comparison with the bilinear interpolation and the tri-linear filter described above.
Japanese Application Publication No. 2010-251,882 discloses an image reproducing apparatus having a feature that, where an input image having M pixels is obtained through image pickup, and where the input image is treated as a resampling target image and is re-sampled, resampling produces a first reducing image and a second reducing image each having M/4 pixels, and such resampling is executed as to create positional deviations of the sampling between the first and second reducing images.